Field of the Invention
The present invention relates to a brushless motor that may be used as a capstan motor for a video player or the like, an operation method therefor and a manufacturing method therefor. More particularly, the present invention relates to a direct pulse width modulation (PWM) brushless motor, an operation method therefor and a manufacturing method therefor.
A typical brushless motor may be used as a capstan motor for a video player or the like that is a main apparatus for the brushless motor. As shown in FIG. 1, the brushless motor is generally composed of a motor main body 11 mounted on a metal substrate 40 and a motor drive circuit (not shown) that drives the motor main body 11. The motor main body 11 has a bearing 20, a rotor shaft 10 rotatably supported by he bearing 20, a rotor 5 capable of rotating with the rotor shaft 10 in one piece, an a stator 30 having cores 32 with driving coils 31 wound around the cores 32. If the motor drive circuit is not provided on the metal rate 40 but is provided on a separate control circuit substrate in the main apparatus (i.e., the video player or the like), the motor main body 11 and the motor drive circuit may need to be connected to each other by wirings. Accordingly, a connector 8 may be mounted on the metal substrate 40 for connecting the motor main body 11 to the motor drive circuit.
FIG. 8 shows an electrical connection structure in the brushless motor 1 in which the motor main body 11 is electrically connected to the motor drive circuit through the connector 8.
Referring to FIG. 8, a motor drive circuit 6 that is equipped with a driver IC 60 is formed with other control circuits for the main apparatus at a location other than the metal substrate 40, such as, for example, in a circuit substrate of the main apparatus. The driver IC 60 has built-in power transistors (i.e., switching elements) Q1-Q4, for example. The motor drive circuit 6 is supplied with a motor power source potential VM, a motor ground potential M.GND, an IC power source potential Vcc and an IC grand potential S.GND. Also, the motor drive circuit 6 and the motor main body 11 are electrically connected to each other through the connector 8 in the following manner. The connector 8 has twelve connector pins 801 through 812. Among the twelve pins, the connector pins 801 through 803 are used for power supply to three driving coils 31 of the motor. The connector pins 804 and 812 are used for supplying the IC power source potential Vcc and the IC grand potential S.GND to three Hall elements H and a sensor FG that is used for speed control of the motor. The connector pins 805 through 811 are used for outputting signals from the Hall elements H or the sensor FG.
In the brushless motor thus structured, the power transistors built in the driver IC 60 are directly turned on and off. Furthermore, the brushless motor uses a direct PWM control system in which the switching pulse width applied to the switching elements is modulated to control current that is conducted through the driving coils.
By the direct PWM control system, the power consumption, which may be wasted through heat generation of the driver IC, is substantially reduced. Therefore, the direct PWM control system is greatly effective in reducing the energy consumption for driving the motor. In addition, the direct PWM control system is effective in reducing the cost because it-can be implemented with almost no additional parts.
A typical direct PWM control system is described with reference to FIGS. 2(A), 2(B), 3 and 4. FIG. 2(A) shows a state of the driver IC 60 of the brushless motor with a direct PWM control system in which power is supplied from a motor power supply source to the driving coils 31. FIG. 2(B) shows a state in which regeneration current flows by a back electromotive force that is generated in the driving coils 31 when the power supply from the motor power supply source to the driving coils 31 is stopped. FIG. 3 shows waveforms of voltage and current that are applied to the driving coils 31 for one phase when the controls shown in FIGS. 2(A) and 2(B) are conducted. FIG. 4 shows waveforms in period a shown in FIG. 3, which includes periods b when voltage is applied to the driving coils 31 and periods c when the voltage supply to the driving coils 31 is stopped. More specifically, FIG. 4 shows a voltage waveform and a current waveform during periods b when a voltage is applied to the driving coils 31 and during periods c when the voltage supply to the driving coils 31 is stopped.
As shown in FIG. 2(A) and FIG. 3, when the power transistor Q4 is in an ON state and the power transistor Q1 is turned ON, the motor power supply potential VM is applied to the driving coils 31 from a motor power supply source 66, such that current flows through the driving coils 31. The current flows through the power transistor Q4 to the motor ground potential M.GND of the motor power supply source 66 (during periods b shown in FIG. 4). As shown in FIG. 4, the current gradually increases in accordance with a time constant of the driving coils 31.
On the other hand, as shown in FIG. 2(B) and FIG. 3, when the power transistor Q4 is in an ON state and the power transistor Q1 is turned OFF, the application of the motor power supply potential VM to the driving coils 31 from the motor power supply source 66 is stopped. At this moment, electromotive forces E1 and E2 are generated in the respective driving coils 31. The electromotive forces E1 and E2 cause regeneration current that flows in the driving coils 31 through a diode 61. The regeneration current gradually decreases in accordance with the time constant of the driving coils 31. However, before the regeneration current completely disappears, the power transistor Q1 is turned ON, and the motor power supply source 66 starts power supply.
In this manner, in the brushless motor using the direct PWM control system, a part of the motor current is supplied by the regeneration current, such that the current (power) to be externally supplied can be cut down. Also, since the power transistors through which the motor current flows are always in a saturated state, the power that may be consumed in the driver IC 60 is reduced to a minimum required level.
However, in the brushless motor using the direct PWM control system, the voltage that is applied to the driving coils 31 shifts between the motor power supply potential VM and the motor ground potential M.GND in a short period of time. As a result, the voltage applied to the wiring that extends from the driver IC 60 to the driving coils 31 or the wiring pattern of the metal substrate 40 as well as the voltage applied to the driving coils 31 continuously repeat rapid shifts, which generates electromagnetic noises. The electromagnetic noises cause a variety of adverse effects on the operation of the main apparatus that uses the brushless motor. Moreover, portions of the metal substrate 40 where the wiring patterns are formed over dielectric layers form capacitive coupling with respect to the driving coils 31 and the wirings, which results in the diffusion of the electromagnetic noises.
In view of the problems described above, it is an object of the present invention to provide a brushless motor using a direct PWM control system, which has a motor driving circuit provided on a circuit substrate that is independent of a motor main body, and which has a structure that can suppress the diffusion of electromagnetic noises.
In accordance with one embodiment of the present invention, a direct PWM brushless motor may have a motor main body mounted on a metal substrate and a motor drive circuit formed on a circuit substrate that is separated from the metal substrate. The motor main body may have a baring, a rotor shaft rotatably supported by the bearing, a rotor capable of rotating with the rotor shaft, and a stator having a core with a driving coil wound around the core. The motor drive circuit includes switching elements that are directly turned on and off. A switching pulse width for the switching elements is modulated to control current conducting through drive coils. In one aspect of the embodiment, the direct PWM brushless motor may have a wiring cable connection device for connecting the motor main body and a fixed potential of the motor drive circuit, and a conduction device that conductively connect a metal plate portion of the metal substrate to the wiring cable connection device.
In accordance with the embodiment of the present invention, the potential of the metal plate portion that defines a substrate of the metal substrate and forms a capacitive coupling with the wiring pattern is fixed at a specified potential through the wiring cable connection device and the conduction device. As a result, when the brushless motor is driven by the direct PWM control method, and the voltage applied to the wiring pattern that extends from the motor driving circuit to the driving coils as well as the voltage applied to the driving coils continuously repeat rapid shifts, electromagnetic noises can be prevented from diffusing through the metal substrate.
In accordance with the present invention, the metal plate of the metal substrate can be connected to the fixed potential through a connector mounted on the metal substrate for connecting the motor main body and the motor drive circuit, a lead wire that is electrically connected to the motor drive circuit, or a tap screw that is fixed at the metal substrate.
When the connector is used, the metal plate portion of the metal substrate can be readily connected to the fixed potential using a cable. When the lead wire is used, the metal plate portion of the metal substrate can be readily connected to the fixed potential without having to modify a connector that has been conventionally used.
The metal plate portion of the metal substrate can be connected to a fixed potential by any one of various methods. For example, a pin of the connector may be directly connected to the metal plate portion, or by connecting through a circuit pattern and a screw.
In accordance with the present invention, the fixed potential may be, for example, a ground potential of the motor drive circuit. Alternatively, the fixed potential may be a power source potential of the motor drive circuit.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.